Federal prosecutors are investigating whether the top executive at Cantor Fitzgerald LP’s gambling unit participated in his company accepting illegal sports bets, according to people familiar with the matter.

The potential alleged involvement of Lee Amaitis—a senior executive at the securities firm who founded Cantor Gaming nine years ago—came to light after a former executive at the unit, Michael Colbert, pleaded guilty to knowingly accepting illegal wagers. His plea was disclosed in federal court documents unsealed late last month.

Cantor Fitzgerald, best known as a bond brokerage, operates sports books through its Cantor Gaming unit. The sports book collects bets on events like football and basketball games in several Nevada casinos. While financial firms have long been major casino investors, the foray into gambling operations was a rare turn. Cantor Gaming has had a rocky start, showing only losses when it has disclosed figures and postponing a planned public offering. As a private partnership, Cantor Fitzgerald doesn’t publicly release financial figures, but the gambling unit’s $7.7 million in reported net revenue for the first nine months of 2011 would be just a sliver of the total revenue for a firm its size.